Nov. 24, 2009 -- New research could help explain how pregnancy protects against breast cancer, and the findings
may one day lead to a novel way to treat the disease.

Investigators from the University of Albany linked the pregnancy protein
alpha-fetoprotein (AFP) to slowed growth of breast cancer in rats exposed to
pregnancy hormones such as estrogen, progesterone, or human chorionic
gonadotropin.

These hormones were shown by the researchers to induce AFP during
pregnancy.

They have also been shown to inhibit breast cancer growth in earlier rat
studies, although estrogen and progesterone are known to fuel the growth of
breast cancer in humans.

Study researcher Herbert Jacobson, PhD, who has been studying AFP in rats
for more than two decades, strongly believes the protein is responsible for the
pregnancy-related reduction in breast cancer risk.

"Twenty-five years ago I deduced that this must be the agent responsible for
lowering breast cancer risk in women who have been pregnant," he tells WebMD.
"And the research we have done since then supports this hypothesis."

AFP and Breast Cancer

Pregnancy, especially before the age of 30, is known to lower a woman's
lifetime risk for developing breast cancer, and having more than one child is
also protective.

Alpha-fetoprotein is made by the fetus, and measurement of the
protein during pregnancy can help screen for birth defects.

Very high AFP levels, for example, suggest the presence of neural tube
defects or an abdominal wall defect known as omphalocele, and very low levels
are suggestive of Down syndrome.

The protein is usually undetectable in the blood of healthy men and healthy
women who aren't pregnant. In these groups, elevated AFP levels suggest the
presence of certain cancers.

In their new study, which appears in the December issue of Cancer
Prevention Research, Jacobson and colleagues treated cancer-exposed rats
that were not pregnant with estrogen, estrogen plus progesterone, or human
chorionic gonadotropin (HCG).

As has been seen in previous studies, all three treatments were associated
with a reduction in breast cancers in the high-risk rats.

All three of the hormone treatments were also associated with elevated AFP
levels and AFP was found to directly inhibit the growth of breast cancer cells
grown in lab cultures.

"Hormones in pregnancy, such as estrogen, all induce AFP, which directly
inhibits the growth of breast cancer," Jacobson says in a news release.

Second Opinion

But cancer specialist Powel Brown, MD, PhD, says the research does not prove
this is the case.

Brown chairs the clinical cancer prevention department at the University of
Texas M.D. Anderson Cancer Center and he serves as an editorial board member
for Cancer Prevention Research.

He called the latest findings promising but preliminary in a statement
released Tuesday.

"The researchers have not directly demonstrated the cancer preventive
activity of AFP," he said, adding that the hormone treatment appeared to
prevent or delay tumors in only 30% to 50% of the rats in the study.

"This study is promising and suggests that additional animal studies need to
be done before translation to humans," he says.

Jacobson says AFP in its natural form is not appropriate for use in humans,
but the research team has identified eight of the hundreds of amino acids in
the protein that might be.

The researchers hope to win approval for early human studies of a modified
version of AFP, which they call AFPep.